Bring lamb to room temperature: Remove the lamb racks from the fridge and season them all over with kosher salt and freshly cracked black pepper. Allow the meat to come to room temperature, about 30 minutes to 1 hour.

Meanwhile, parboil the potatoes. Add potatoes to a large pot of cold, salted water. Cook over medium heat until tender, about 15-20 minutes. Drain potatoes and place on a large baking sheet.

Make Lamb Marinade: Add Dijon mustard, garlic cloves, ¼ cup olive oil, and 2 tablespoons rosemary leaves to a food processor and process until finely chopped and combined.

Heat the oven to 425 degrees F and place oven rack on the top ⅓ of the oven.

Sear Lamb Racks: Heat a large cast iron pot over medium-high heat. Add 2 tablespoons olive oil to lightly coat the bottom of the pan. Once hot, add lamb racks, fat side down first. Sear for 1-2 minutes on each sides.

Smash Potatoes: Use the back of a spoon to gently smash the potatoes flat. Drizzle them with 1-2 tablespoons extra virgin olive oil, and season with a little kosher salt and pepper. Sprinkle remaining 1 tablespoon rosemary over potatoes.

Prepare to Roast: Lay the seared lamb racks on top of the potatoes, with the bones curving downwards (fat side up). Optional, wrap the exposed end of the rib bones in foil, for a prettier appearance when serving. Spoon the lamb marinade over the lamb racks.

Roast, uncovered, for 15-25 minutes, until a meat thermometer registers 120-130 degrees F for rare, or 130-140 degrees F for medium rare. I suggest removing from oven when it reaches 5 degrees below your desired temperature, since the meat will continue to cook as it rests.

Rest: Remove lamb to a cutting board and tent with foil. Allow to rest for 15 minutes before serving.

Crisp Potatoes: Return potatoes to oven and roast for 10 more minutes, until crispy.

To serve, cut the lamb in between the bones and transfer to a serving platter with the potatoes. Sprinkle with fresh parsley. Serve 2-3 chops per person.